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    Messed Up My Install

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    NuttyLemur

    Posts : 18
    Join date : 2013-06-29

    Messed Up My Install

    Post by NuttyLemur on Wed Sep 11, 2013 1:34 am

    Just finished installing my new VTA board and I only have bias/current through the rear left tube. I checked to see if the bias checking pins on the front of the amp were good, got 10 ohms across all of them.

    should have left the amp alone I was happy before Sad 

    any suggestions would be awesome.

    oh yeah, also tried to listen to some music only got music from the left speaker.

    NuttyLemur

    Posts : 18
    Join date : 2013-06-29

    Re: Messed Up My Install

    Post by NuttyLemur on Wed Sep 11, 2013 1:36 am

    I also checked to see if I had voltage across pin 6 of each tube, had just under 40v over each.

    Zimmer64

    Posts : 113
    Join date : 2013-01-29
    Age : 52
    Location : Switzerland

    Re: Messed Up My Install

    Post by Zimmer64 on Wed Sep 11, 2013 6:16 am

    Check systematically against the manual. Double check all wiring, solder joints etc. Are all parts at the right place? Post a picture of your work. This makes it easier for others to come up with help. Hope you find the error soon.

    Michael

    arledgsc

    Posts : 340
    Join date : 2012-11-30
    Location : SF Bay CA

    Re: Messed Up My Install

    Post by arledgsc on Wed Sep 11, 2013 10:49 am

    A bias voltage issue should one of the easiest problems to isolate.  Other than the VTA board exchange I am assuming that no other wiring in amp changed and use to work OK with the older board.   First double check all the VTA board part installations (electrolytic cap orientation, resistor values/locations, and VTA board properly screwed down to the chassis making the ground connection), wiring, and solder quality.  Remove all tubes and rectifier tube or sub, set the four bias voltage adjustment pots to mid-range, turn the amp on, and check the bias voltage feeds (all negative DC values below ground potential).  Since you have two identical circuits (left and right) you can generally go back and forth at similar circuit stages for comparison (since left rear seems to work somewhat).  Start at the diode rectifier and work your way through bias voltage circuits comparing left and right readings as they should be very close.  When the voltages differ concentrate on that part of the circuit to understand why.  You have no high voltage or tubes installed using this basic debug method so if the bias voltages look OK at this point you may have a bad component like a coupling capacitor... But first things first - do the basics and work your way up....

    I just thought of something else to check first.  When mounting the VTA board you did place nut spacers underneath the board?  This adds needed clearance between the VTA board and chassis or otherwise you could short out the bias voltages and audio signal before they get to the output tubes.   With no power applied check continuity (ohmage) of the wire feeding output to grid from the VTA board (output tube pin 5 to ground).   Normally they should read each about 50K ohms with the bias pots set mid-range.  WARNING:  No power is applied and the high voltage capacitors allowed to bleed before attempting.

    sKiZo

    Posts : 1310
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Messed Up My Install

    Post by sKiZo on Wed Sep 11, 2013 4:45 pm

    Also check to make sure the coupling caps aren't shorting out on the chassis? Pretty close in there ...

    NuttyLemur

    Posts : 18
    Join date : 2013-06-29

    Re: Messed Up My Install

    Post by NuttyLemur on Wed Sep 11, 2013 7:38 pm


    NuttyLemur

    Posts : 18
    Join date : 2013-06-29

    Re: Messed Up My Install

    Post by NuttyLemur on Wed Sep 11, 2013 7:41 pm

    rechecked to make sure nothing is grounded out wrong and checked against the wiring picture on the website. hopefully the picture is good enough someone can quickly tell me what I did wrong.

    NuttyLemur

    Posts : 18
    Join date : 2013-06-29

    Re: Messed Up My Install

    Post by NuttyLemur on Wed Sep 11, 2013 7:44 pm



    driver board.

    NuttyLemur

    Posts : 18
    Join date : 2013-06-29

    Re: Messed Up My Install

    Post by NuttyLemur on Wed Sep 11, 2013 8:03 pm

    How do I know if I got the coupling caps in right? (Those are the big silver ones on the bottom, correct?) I see markings on them but I don't understand it.

    Hopefully I didn't destroy them. They don't look damaged.

    kaner

    Posts : 88
    Join date : 2011-09-20

    Re: Messed Up My Install

    Post by kaner on Wed Sep 11, 2013 9:30 pm

    At least you got music from one side. Use that side to check the side that's not working. Look for caps with their ground on the wrong side, check resistor values, use the continuity setting on your DVM to check your solder joints. Don't be discouraged. All of us have made mistakes. It's a RARE amp build that works right on the first try. In fact, most if not all of us will check each solder joint, each capacitor, each resistor and each transformer hookup carefully before we ever apply any power. Then we realize something is not right, do the detective work to fix it and try again. Even then we'll bring it up slowly and monitor the results.

    Don't be discouraged. When you get it working, you will have a real sense of accomplishment.

    kaner

    Posts : 88
    Join date : 2011-09-20

    Re: Messed Up My Install

    Post by kaner on Wed Sep 11, 2013 9:39 pm

    By the way, yes those are the coupling caps. You do need to be careful with those big PIO's to make sure that the leads aren't touching the chassis and that the body of the cap isn't leaning across anything on the board. Most components are pretty tough. I doubt you ruined anything. Take your time and check, check and re-check.

    kaner

    Posts : 88
    Join date : 2011-09-20

    Re: Messed Up My Install

    Post by kaner on Thu Sep 12, 2013 8:32 am

    Another thought on your coupling caps. Make sure that the leads aren't touching the body of the cap. An easy solution is to strip an inch of insulation off of a wire & slip it over the leads on the cap. You will need to take them out to do it, but then you won't need to worry about shorting the leads. Also, note that on the board itself there are options to where you solder them in. Use the outermost set for those big caps.

    Zimmer64

    Posts : 113
    Join date : 2013-01-29
    Age : 52
    Location : Switzerland

    Re: Messed Up My Install

    Post by Zimmer64 on Thu Sep 12, 2013 9:29 am

    I can't see much on your pics. You may want to compare to mine: http://zimmer64.wordpress.com/tag/dynaco-st-70/ look at entry "2" and "7". There are lots of high rez pictures (if you click on them) that you can use for comparison. As kaner already said make sure those coupling caps are not touching anything conductive. Not even their own leads.

    NuttyLemur

    Posts : 18
    Join date : 2013-06-29

    Re: Messed Up My Install

    Post by NuttyLemur on Sat Sep 14, 2013 9:09 pm

    Went back through checking everything. Now I get about .017-.025v across the bias.

    Any other suggestions?

    NuttyLemur

    Posts : 18
    Join date : 2013-06-29

    Re: Messed Up My Install

    Post by NuttyLemur on Sat Sep 14, 2013 9:28 pm

    I do get sound out both sides now. Found a wire with a bad connection.

    Had it on for a few seconds and it started making a loud buzz/hum sound, so I killed it quickly.

    corndog71

    Posts : 451
    Join date : 2013-03-19
    Location : It can get windy here

    Re: Messed Up My Install

    Post by corndog71 on Sun Sep 15, 2013 9:02 pm

    Go over every connection again. Don't assume anything. Leave it alone for a week or two then go over it all over again with fresh eyes.

    Worst case scenario: you damaged your tubes. I've done it. It really sucks. But all you can do is go over the amp and make absolutely certain the wires go where they're supposed to before plugging any more tubes in there.

    NuttyLemur

    Posts : 18
    Join date : 2013-06-29

    Re: Messed Up My Install

    Post by NuttyLemur on Mon Sep 16, 2013 12:18 pm

    Got it playing now, but the bias is still weird and when played at moderate levels the guitars and snares sound "crunchy" for a lack of better terms. I rechecked my resistors thinking I might have 1 or.1 ohm resistors in the bias location instead of the 10s. Everything checks out. I think I am going to let it sit like suggested and come ack with fresh perspective.

    Man already have 2 weeks without my records, bummer. I have an Emotiva amp, but it doesn't sound the same.

    Zimmer64

    Posts : 113
    Join date : 2013-01-29
    Age : 52
    Location : Switzerland

    Re: Messed Up My Install

    Post by Zimmer64 on Mon Sep 16, 2013 1:42 pm

    Do not despair. corndog71 is right. Check everything again after a little break. You will get there.

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